华东地质2025，Vol.46Issue(1)：55-67,13.DOI:10.16788/j.hddz.32-1865/P.2023.12.011
渤南洼陷沙四下亚段微量元素地球化学特征及其对沉积环境的指示
Geochemical characteristics of trace elements in the Es4x Formation of the Bonan Sag and their implications for sedimentary environment
摘要
Abstract
The Bonan Sag is an important oil and gas-rich region of Bohai Bay basin.In order to clarify the depositional environment and hydrocarbon potential of the hydrocarbon source rocks in the lower subsection of Es4x in the Bonan Sag,and the hydrocarbon potential of the hydrocarbon source rocks of the Es4x,we analyzed the typical mudstone samples of the Es4x in the Bonan Sag by trace element testing and organic geochemical charac-teristics.Through selecting the elements and element combinations sensitive to the depositional environment,such as δCen,Ceanom,Ni/Co,V/Ni,V/(V+Ni),V/Cr,B/Ga etc.,in combination with the organic geochemical character-istics,this paper clarified the climate,redox environment and salinity during the sedimentary period of the Es4x in the Bonan Sag.The applicability of these parameters in the paleoenvironment study for the working area and the factors affecting the development of source rocks with hydrocarbon generation potential were discussed.The re-sults show that the Lan/Ybn values range from 1.62 to 3.00;B/Ga range from 1.43 to 3.73;the blackish mudstones have Pr/Ph＜1,δCen＞1,and Ceanom＞0,and the reddish mudstones samples have δCen values ranging from 0.94 to 0.96,and Ceanom＜0.It indicates a warm and humid climate in some areas during the depositional period of the Es4x in the Bonan Sag,a slow sediment deposition rate,and a freshwater-slightly saline environment of the whole area,while that part of the area was in an anoxic environment,except for the oxygen-rich environment.The results of comparative analysis show that using δCen and Ceanom is reliable to discriminate redox environments,and the rela-tive magnitudes of mudstone Ni/Co,V/Ni,and V/(V+Ni)can infer the anoxicity of environment during their de-position,and the B/Ga ratio can distinguish freshwater-brackish water and brackish water environment.In addi-tion,the mudstone in the study area of the Es4x has a high content of sapropelinite,the kerogen is type II-III;TOC,S1+S2,and chloroform bitumen"A"contents of some mudstones indicate that they have reached the level of general hydrocarbon source rocks.Compared with the non-hydrocarbon source rock in the study area,they have smaller B/Ga and larger ETR index and gammacerane index.This suggests that the development of hydrocarbon-generating potential source rocks in anoxic environments may depend on the salinity of the sedimentary water.关键词
渤南洼陷/沙四下亚段/微量元素/沉积环境Key words
Bonan Sag/Es4x/trace element/sedimentary environment分类
地质学引用本文复制引用
张波,郭晓英,孟涛,姜超,刘鹏,陈勇..渤南洼陷沙四下亚段微量元素地球化学特征及其对沉积环境的指示[J].华东地质,2025,46(1):55-67,13.基金项目
中国石化科技部"济阳坳陷近源领域成藏体系评价与目标优选(编号:P22066)"项目资助. （编号:P22066）
